Browsing by Author "Ossandon, Tomas"
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- ItemA Visuospatial Planning Task Coupled with Eye-Tracker and Electroencephalogram Systems(2023) Domic Siede, Marcos; Irani, Martin; Valdes, Joaquin; Rodriguez, Maria; Follet, Brice; Perrone-Bertolotti, Marcela; Ossandon, TomasThe planning process, characterized by the capability to formulate an organized plan to reach a goal, is essential for human goal-directed behavior. Since planning is compromised in several neuropsychiatric disorders, the implementation of proper clinical and experimental tests to examine planning is critical. Due to the nature of the deployment of planning, in which several cognitive domains participate, the assessment of planning and the design of behavioral paradigms coupled with neuroimaging methods are current challenges in cognitive neuroscience. A planning task was evaluated in combination with an electroencephalogram (EEG) system and eye movement recordings in 27 healthy adult participants. Planning can be separated into two stages: a mental planning stage in which a sequence of steps is internally represented and an execution stage in which motor action is used to achieve a previously planned goal. Our protocol included a planning task and a control task. The planning task involved solving 36 maze trials, each representing a zoo map. The task had four periods: i) planning, where the subjects were instructed to plan a path to visit the locations of four animals according to a set of rules; ii) maintenance, where the subjects had to retain the planned path in their working memory; iii) execution, where the subjects used eye movements to trace the previously planned path as indicated by the eye-tracker system; and iv) response, where the subjects reported the order of the visited animals. The control task had a similar structure, but the cognitive planning component was removed by modifying the task goal. The spatial and temporal patterns of the EEG revealed that planning induces a gradual and lasting rise in frontal-midline theta activity (FM?) over time. The source of this activity was identified within the prefrontal cortex by source analyses. Our results suggested that the experimental paradigm combining EEG and eye-tracker systems was optimal for evaluating cognitive planning.
- ItemBrain activity complexity has a nonlinear relation to the level of propofol sedation(2021) Boncompte, Gonzalo; Medel, Vicente; Cortinez, Luis, I; Ossandon, TomasBackground: Brain activity complexity is a promising correlate of states of consciousness. Previous studies have shown higher complexity for awake compared with deep anaesthesia states. However, little attention has been paid to complexity in intermediate states of sedation.
- ItemDysconnectivity in Schizophrenia Revisited: Abnormal Temporal Organization of Dynamic Functional Connectivity in Patients With a First Episode of Psychosis(2023) Ramirez-Mahaluf, Juan P.; Tepper, Angeles; Maria Alliende, Luz; Mena, Carlos; Castaneda, Carmen Paz; Iruretagoyena, Barbara; Nachar, Ruben; Reyes-Madrigal, Francisco; Leon-Ortiz, Pablo; Mora-Duran, Ricardo; Ossandon, Tomas; Gonzalez-Valderrama, Alfonso; Undurraga, Juan; De la Fuente-Sandoval, Camilo; Crossley, Nicolas A.Background and Hypothesis Abnormal functional connectivity between brain regions is a consistent finding in schizophrenia, including functional magnetic resonance imaging (fMRI) studies. Recent studies have highlighted that connectivity changes in time in healthy subjects. We here examined the temporal changes in functional connectivity in patients with a first episode of psychosis (FEP). Specifically, we analyzed the temporal order in which whole-brain organization states were visited. Study Design Two case-control studies, including in each sample a subgroup scanned a second time after treatment. Chilean sample included 79 patients with a FEP and 83 healthy controls. Mexican sample included 21 antipsychotic-naive FEP patients and 15 healthy controls. Characteristics of the temporal trajectories between whole-brain functional connectivity meta-states were examined via resting-state functional MRI using elements of network science. We compared the cohorts of cases and controls and explored their differences as well as potential associations with symptoms, cognition, and antipsychotic medication doses. Study Results We found that the temporal sequence in which patients' brain dynamics visited the different states was more redundant and segregated. Patients were less flexible than controls in changing their network in time from different configurations, and explored the whole landscape of possible states in a less efficient way. These changes were related to the dose of antipsychotics the patients were receiving. We replicated the relationship with antipsychotic medication in the antipsychotic-naive FEP sample scanned before and after treatment. Conclusions We conclude that psychosis is related to a temporal disorganization of the brain's dynamic functional connectivity, and this is associated with antipsychotic medication use.
- ItemEfficient "Pop-Out" Visual Search Elicits Sustained Broadband Gamma Activity in the Dorsal Attention Network(2012) Ossandon, Tomas; Vidal, Juan R.; Ciumas, Carolina; Jerbi, Karim; Hamame, Carlos M.; Dalal, Sarang S.; Bertrand, Olivier; Minotti, Lorella; Kahane, Philippe; Lachaux, Jean-PhilippeAn object that differs markedly from its surrounding-for example, a red cherry among green leaves-seems to pop out effortlessly in our visual experience. The rapid detection of salient targets, independently of the number of other items in the scene, is thought to be mediated by efficient search brain mechanisms. It is not clear, however, whether efficient search is actually an "effortless" bottom-up process or whether it also involves regions of the prefrontal cortex generally associated with top-down sustained attention. We addressed this question with intracranial EEG (iEEG) recordings designed to identify brain regions underlying a classic visual search task and correlate neural activity with target detection latencies on a trial-by-trial basis with high temporal precision recordings of these regions in epileptic patients. The spatio-temporal dynamics of single-trial spectral analysis of iEEG recordings revealed sustained energy increases in a broad gamma band (50-150 Hz) throughout the duration of the search process in the entire dorsal attention network both in efficient and inefficient search conditions. By contrast to extensive theoretical and experimental indications that efficient search relies exclusively on transient bottom-up processes in visual areas, we found that efficient search is mediated by sustained gamma activity in the dorsal lateral prefrontal cortex and the anterior cingulate cortex, alongside the superior parietal cortex and the frontal eye field. Our findings support the hypothesis that active visual search systematically involves the frontal-parietal attention network and therefore, executive attention resources, regardless of target saliency.
- ItemFunctional selectivity in the human occipitotemporal cortex during natural vision: Evidence from combined intracranial EEG and eye-tracking(2014) Hamame, Carlos M.; Vidal, Juan R.; Perrone-Bertolotti, Marcela; Ossandon, Tomas; Jerbi, Karim; Kahane, Philippe; Bertrand, Olivier; Lachaux, Jean-PhilippeEye movements are a constant and essential component of natural vision, yet, most of our knowledge about the human visual system comes from experiments that restrict them. This experimental constraint is mostly in place to control visual stimuli presentation and to avoid artifacts in non-invasive measures of brain activity, however, this limitation can be overcome with intracranial EEG (iEEG) recorded from epilepsy patients. Moreover, the high-frequency components of the iEEG signal (between about 50 and 150 Hz) can provide a proxy of population-level spiking activity in any cortical area during free-viewing. We combined iEEG with high precision eye-tracking to study fine temporal dynamics and functional specificity in the fusiform face (FFA) and visual word form area (VWFA) while patients inspected natural pictures containing faces and text. We defined the first local measure of visual (electrophysiological) responsiveness adapted to free-viewing in humans: amplitude modulations in the high-frequency activity range (50-150 Hz) following fixations (fixation-related high-frequency response). We showed that despite the large size of receptive fields in the ventral occipito-temporal cortex, neural activity during natural vision of realistic cluttered scenes is mostly dependent upon the category of the foveated stimulus - suggesting that category-specificity is preserved during free-viewing and that attention mechanisms might filter out the influence of objects surrounding the fovea. (C) 2014 Elsevier Inc. All rights reserved.
- ItemHow Silent Is Silent Reading? Intracerebral Evidence for Top-Down Activation of Temporal Voice Areas during Reading(2012) Perrone-Bertolotti, Marcela; Kujala, Jan; Vidal, Juan R.; Hamame, Carlos M.; Ossandon, Tomas; Bertrand, Olivier; Minotti, Lorella; Kahane, Philippe; Jerbi, Karim; Lachaux, Jean-PhilippeAs you might experience it while reading this sentence, silent reading often involves an imagery speech component: we can hear our own "inner voice" pronouncing words mentally. Recent functional magnetic resonance imaging studies have associated that component with increased metabolic activity in the auditory cortex, including voice-selective areas. It remains to be determined, however, whether this activation arises automatically from early bottom-up visual inputs or whether it depends on late top-down control processes modulated by task demands. To answer this question, we collaborated with four epileptic human patients recorded with intracranial electrodes in the auditory cortex for therapeutic purposes, and measured high-frequency (50 - 150 Hz) "gamma" activity as a proxy of population level spiking activity. Temporal voice-selective areas (TVAs) were identified with an auditory localizer task and monitored as participants viewed words flashed on screen. We compared neural responses depending on whether words were attended or ignored and found a significant increase of neural activity in response to words, strongly enhanced by attention. In one of the patients, we could record that response at 800 ms in TVAs, but also at 700 ms in the primary auditory cortex and at 300 ms in the ventral occipital temporal cortex. Furthermore, single-trial analysis revealed a considerable jitter between activation peaks in visual and auditory cortices. Altogether, our results demonstrate that the multimodal mental experience of reading is in fact a heterogeneous complex of asynchronous neural responses, and that auditory and visual modalities often process distinct temporal frames of our environment at the same time.
- ItemHuman Anterior Insula Encodes Performance Feedback and Relays Prediction Error to the Medial Prefrontal Cortex(2020) Billeke, Pablo; Ossandon, Tomas; Perrone-Bertolotti, Marcela; Kahane, Philippe; Bastin, Julien; Jerbi, Karim; Lachaux, Jean-Philippe; Fuentealba, PabloAdaptive behavior requires the comparison of outcome predictions with actual outcomes (e.g., performance feedback). This process of performance monitoring is computed by a distributed brain network comprising the medial prefrontal cortex (mPFC) and the anterior insular cortex (AIC). Despite being consistently co-activated during different tasks, the precise neuronal computations of each region and their interactions remain elusive. In order to assess the neural mechanism by which the AIC processes performance feedback, we recorded AIC electrophysiological activity in humans. We found that the AIC beta oscillations amplitude is modulated by the probability of performance feedback valence (positive or negative) given the context (task and condition difficulty). Furthermore, the valence of feedback was encoded by delta waves phase-modulating the power of beta oscillations. Finally, connectivity and causal analysis showed that beta oscillations relay feedback information signals to the mPFC. These results reveal that structured oscillatory activity in the anterior insula encodes performance feedback information, thus coordinating brain circuits related to reward-based learning.
- ItemSemi-Automated and Direct Localization and Labeling of EEG Electrodes Using MR Structural Images for Simultaneous fMRI-EEG(2020) Bhutada, Abhishek S.; Sepulveda, Pradyumna; Torres, Rafael; Ossandon, Tomas; Ruiz, Sergio; Sitaram, RanganathaElectroencephalography (EEG) source reconstruction estimates spatial information from the brain's electrical activity acquired using EEG. This method requires accurate identification of the EEG electrodes in a three-dimensional (3D) space and involves spatial localization and labeling of EEG electrodes. Here, we propose a new approach to tackle this two-step problem based on the simultaneous acquisition of EEG and magnetic resonance imaging (MRI). For the step of spatial localization of electrodes, we extract the electrode coordinates from the curvature of the protrusions formed in the high-resolution T1-weighted brain scans. In the next step, we assign labels to each electrode based on the distinguishing feature of the electrode's distance profile in relation to other electrodes. We then compare the subject's electrode data with template-based models of prelabeled distance profiles of correctly labeled subjects. Based on this approach, we could localize EEG electrodes in 26 head models with over 90% accuracy in the 3D localization of electrodes. Next, we performed electrode labeling of the subjects' data with progressive improvements in accuracy: with similar to 58% accuracy based on a single EEG-template, with similar to 71% accuracy based on 3 EEG-templates, and with similar to 76% accuracy using 5 EEG-templates. The proposed semi-automated method provides a simple alternative for the rapid localization and labeling of electrodes without the requirement of any additional equipment than what is already used in an EEG-fMRI setup.